This invention relates to a multi jet propelled watercraft and more particularly an improved jet propulsion unit for utilization in such a watercraft.
The copending application of Noboru Kobayashi, entitled "Watercraft With A Couple Of Water Jet Propulsion Units", Ser. No. 544,404, filed June 27, 1990, discloses a number of embodiments of watercraft having V hulls and in which a pair of jet propulsion units are employed for powering the watercraft. That type of watercraft has a great degree of utility. However, there are certain features in connection with such type of watercraft which can be improved upon. These features may be best understood by reference to FIG. 1 which is a cross sectional view taken through the tunnel portion of a watercraft having a V hull and a pair of jet propulsion units for operating the watercraft. As may be seen, the watercraft has a hull that is shown partially and is indicated generally by the reference numeral 11, which has a V bottom defined by a pair of angularly disposed lower surfaces 12 and 13. A tunnel 14 is provided in this hull at the rear end thereof and supports a pair of jet propulsion units 15 in side by side relationship.
As is noted in the copending application, there are a number of advantages in mounting the jet propulsion units 15 so that they can be raised and lowered to raise and lower the water inlet openings 16 of the jet propulsion units out of the body of water in which the watercraft is operating. In some instances, it is also desireable to rotate the water inlet portions 16 from their downwardly facing positions to an upwardly facing position so that the water inlet opening can be accessed for servicing through the hull of the watercraft by an access opening which is not shown in FIG. 1.
The raising and lowering of the jet propulsion units 15 is accomplished by pairs of hydraulic cylinders 17 which are connected to the jet propulsion units 15 in the manner described in the aforenoted application.
In the noted copending application, there a number of variations in tunnel arrangements disclosed. It will be noted that all of these tunnel arrangements require the jet propulsion units 15 to be spaced apart at a fairly substantial distance. The reason for this is to insure clearance between the jet propulsion units when they are raised to their elevated positions, as shown in phantom in FIG. 1. FIG. 1 clearly shows how interference can be encountered when the tunnel 14 is kept narrow, as is obviously desirable.
In addition, each jet propulsion unit 15 has a steering nozzle 18 which is supported for steering movement about a steering axis that is defined by a pair of pivot pins 19 which pivotally connect the steering nozzle 18 to the discharge nozzle of the jet propulsion unit 15. As may be readily seen, the jet propulsion units 15 are normally designed to operate so that the steering axes 19 are vertically disposed. However, when two such units are mounted in a V bottom hull and the water inlet opening 16 extends parallel to the hull surfaces 12 and 13, then the pivot axes of the steering nozzles become skewed and perpendicular to the surfaces 12 and 13, respectively.
As may be seen by the phantom line view of FIG. 1 wherein the nozzles are depicted toward a right hand steering position, the angular disposition of the pivot axes will give rise to not only steering thrusts, but thrusts that act in a vertical direction. Because of the opposite angular disposition, these vertical thrusts will be in opposite directions and tend to cause the generation of a turning moment on the watercraft 11, which is obviously undesirable.
It is, therefore, a principal object of this invention to provide an improved twin jet propulsion unit for a watercraft and particularly one having a V hull.
It is a further object of this invention to provide a twin jet propulsion unit for a watercraft having a V hull and in which a compact tunnel may be employed to contain both jet propulsion units.
It is a further object of this invention to provide a twin jet propulsion unit for a V hull watercraft that permits the jet propulsion units to be easily lifted relative to the body of water in which the watercraft is operating without interference.
It is a further object of this invention to provide an improved twin jet propulsion drive for a V bottom watercraft wherein steering can be accomplished without generating lifting or turning forces on the hull.